Are we pushing animals over the edge?

(Press-News.org) Species of mammals and birds are threatened with extinction as a result of rising human population density, according to Jeffrey McKee and colleagues from The Ohio State University in the US. Their work is also the first to show that the exponential growth of the human population will continue to pose a threat to other species. In other words, there does not appear to be a threshold above which population growth would cease to have an incremental negative effect. The study is published online in Springer's journal, Human Ecology.

It has long been suspected that the number of threatened species today could be linked to the size, density and growth of the human population. McKee and team set out to prove a causal link between human population density and threats to species of mammals and birds that can be quantified, not only at present, but as the human population grows.

To both validate their hypothesis and make projections about future effects of population growth on threatened species, the researchers used US Census Bureau data from 2000, 2010 and projected population sizes for 2020 and 2050, for 114 countries. At the same time, they compiled data on threatened mammal and bird species from the IUCN Red List of Threatened Species*.

They found that changes in human population density had measurable consequences on changes in the number of threatened species by nation. The average nation with a growing population can expect a 3.3 percent increase in the number of threatened mammals and birds over the next decade, and a 10.8 percent increase by 2050, based on human population growth alone.

No apparent threshold effect to reduce further risks to biodiversity was identified, suggesting that future conservation efforts should take human population density into account at the outset. Conservation efforts could be focused in countries in which human population is decreasing. Such areas could be targeted for wild land reclamation and reconstitution of other native species that remain threatened.

The authors conclude: "There is no doubt that a multitude of factors go into diminishing the availability of resources that mammals and birds need to survive as viable species. Our results demonstrate that human population density is at the core of extinction threats to both mammals and birds."

### * The IUCN Red List of Threatened Species™ is a comprehensive, objective global approach for evaluating the conservation status of plant and animal species.

Reference McKee J et al (2013). Human Population Density and Growth Validated as Extinction Threats to Mammal and Bird Species. Human Ecology; DOI 10.1007/s10745-013-9586-8

The full-text article is available to journalists on request.